Remove ASLayoutChild. ASLayout now has a position property defaults to (NAN, NAN).

AsyncDisplayKit/Layout/ASLayout.mm

@@ -9,39 +9,53 @@
  */
 
 #import "ASLayout.h"
+#import "ASAssert.h"
+
+CGPoint const CGPointNull = {NAN, NAN};
+
+extern BOOL CGPointIsNull(CGPoint point)
+{
+  return isnan(point.x) && isnan(point.y);
+}
 
 @implementation ASLayout
 
 + (instancetype)newWithLayoutableObject:(id<ASLayoutable>)layoutableObject
                                    size:(CGSize)size
+                               position:(CGPoint)position
                                children:(NSArray *)children
 {
+  for (ASLayout *child in children) {
+    ASDisplayNodeAssert(!CGPointIsNull(child.position), @"Invalid position is not allowed in children.");
+  }
+  
   ASLayout *l = [super new];
   if (l) {
     l->_layoutableObject = layoutableObject;
     l->_size = size;
+    l->_position = position;
     l->_children = [children copy];
   }
   return l;
 }
 
++ (instancetype)newWithLayoutableObject:(id<ASLayoutable>)layoutableObject
+                                   size:(CGSize)size
+                               children:(NSArray *)children
+{
+  return [self newWithLayoutableObject:layoutableObject size:size position:CGPointNull children:children];
+}
+
 + (instancetype)newWithLayoutableObject:(id<ASLayoutable>)layoutableObject size:(CGSize)size
 {
   return [self newWithLayoutableObject:layoutableObject size:size children:nil];
 }
 
-@end
-
-@implementation ASLayoutChild
-
-+ (instancetype)newWithPosition:(CGPoint)position layout:(ASLayout *)layout
+- (void)setPosition:(CGPoint)position
 {
-  ASLayoutChild *c = [super new];
-  if (c) {
-    c->_position = position;
-    c->_layout = layout;
-  }
-  return c;
+  ASDisplayNodeAssert(CGPointIsNull(_position), @"Position can be set once and only once.");
+  ASDisplayNodeAssert(!CGPointIsNull(position), @"Position must not be set to null.");
+  _position = position;
 }
 
 @end